1. Field of the Invention
The present invention relates to a transmitting optical module, in particular, the invention relates to an optical module with a ceramic package.
2. Related Prior Art
The United States patent, U.S. Pat. No. 7,476,040B, has disclosed an optical module with a multi-layered ceramic package installing a sub-mount, a light-transmitting device with a type of, what is called, vertical cavity surface emitting laser diode (VCSEL) mounted on the sub-mount and a lens arranged above the sub-mount and secured by the package. The light emitted from the surface of the VCSEL is directly coupled with the optical fiber, which is also arranged above the package, though the lens.
The optical module like those disclosed in the prior art above sometimes installs a semiconductor laser diode (hereafter denoted as LD) of the edge-emitting type. In such an optical module, the light emitted from the LD is necessary to be reflected by an optical component such as mirror and prism to couple the light with the optical fiber arranged above the package. The optical coupling efficient between the LD and the optical fiber in such a module with a bent optical axis therebetween depends on the optical design, in particular, a distance between the LD and the lens strongly influences on the optical coupling efficiency.
Various factors affects the optical coupling efficiency between the LD and the optical fiber; for instance, (1) positional accuracy between the LD and the sub-mount, (2) a distance between the sub-mount and the optical component to reflect light, (3) a distance between the light-reflecting surface of the optical component and the lens, and so on. The first factor above listed may be overcome by the assembling process using a device-mounting apparatus. Specifically, the apparatus may position the LD relative to the sub-mount which is fixed with respect to the apparatus by carrying the LD after abutting it to the reference plane of the apparatus; while, the forming accuracy of the optical component, that of the housing of the module, and that of the lens solely influence the positional tolerance between the lens and the optical component.
However, the positional accuracy between the sub-mount and the optical component, which is listed as the second factor above, is necessary to assemble the optical component relative to the sub-mount, on which the LD is mounted, with a designed distance therebetween. This process requires an advanced apparatus that provides an image recognition system to align the position of the element, such as the LD, the optical component and the sub-mount.